The invention relates to a process and the associated device for the fine crushing of mineral and non-mineral substances, preferably cement raw materials and cement clinker, by single or repeated compressive-load application using medium to high pressures (60 to 300 bar/6 to 30 Mpa) with subsequent disagglomeration of the produced ground material on the same device.
The fine crushing of mineral and non-mineral substances, such as e.g. cement raw materials or cement clinkers, is normally carried out in tubular ball and rolling mills and recently also in high-pressure crushing rollers. Although high-pressure crushing rollers have displaced the tubular mill in recent years because of their better utilization of energy, this mill, in which the compressive-load is applied to the material using high to very high pressure forces, can still be improved.
The compressive crushing of material layers in a high-pressure crushing roller, called material-bed rolling mill according to DE-B2-27 08 053 and characterized essentially in that the crushing is carried out by a single compressive-load application between two surfaces at pressures well above 50 MPa in the gap between two cylindrical rolls driven in opposite directions, has decisive disadvantages.
Firstly, high-pressure crushing rollers operate at very high pressures, i.e. with relative pressing forces between 10 to 20 kN/mm load-application range which lie many times higher than with other crushing machines using pressure mechanisms. The freedom to set these pressing forces is limited, as the mill, for reasons of vibration, must always be operated in the border range of its load-application over a level-controlled material bunker, comparable to the operation of a compacting press. The operation of the mill in this border range is, depending on the material, already characterized by the onset of a consolidation of the material layer to which the load is applied and characterized by a dis-proportionally high energy consumption in relation to the production of fine material, which normally rises linearly up to pressures of 50 MPa, but comes to a stop when a further load is applied. The use of high to very high pressing forces leads to a very heavy machine structure and a costly roller bearing system with complicated bearing lubrication and bearing cooling. Torque peaks, caused by foreign bodies, by skewing of the moving roller or by ventilation problems, can lead to serious damage on the armoured load-application surfaces of the rollers, to bearings, transmission elements and gears. The wear of the load-application surfaces, which often achieve service lives of only 5,000 operating hours, depending on the abrasivity of the material to be ground, is also problematic.
Secondly, high-pressure crushing rollers have an unfavourable throughput-to-speed behaviour. The throughput characteristic line of a pair of rollers charged by a feed bunker is non-linear, i.e., depending on the material properties and the geometry of the load-application surfaces, the throughput can drop by up to 50% with increasing circumferential speed. In addition, the fitted material bunker is not in a position to mix the fresh material with the recycling material and feed them to the roller gap in the mass flow, i.e. the load applied at the roller gap is in no way defined. Because of this fact and bearing in mind the vibration behaviour of the mill, which also depends very much on the particle size composition of the feed material and deteriorates with increasing speed, the circumferential speeds of high-pressure crushing rollers which are achievable in practice lie in general only between 1.0 and 1.8 m/s. The throughput of high-pressure crushing rollers thus remains limited. Large throughputs are therefore possible only through the widening of the grinding rollers with a proportional increase in the pressing forces, which is however limited in terms of machine technology.
Thirdly, high-pressure crushing rollers always lead to a multi-stage technology inside a crushing plant, as it carries out only preliminary crushing during most applications and has to be connected, via external transport routes, to appropriate apparatuses for the disaglomeration, separating, final crushing and drying of the ground material. The machine-, construction- and control-related expenditure for a crushing plant with high-pressure crushing rollers is not therefore generally lower than when using other mills. (Feige, F.: Entwicklungsstand der Hockdruckzerkleinerung, ZKG INTERNATIONAL 46 (1993) No. 9, p. 586-595).
The object of the invention is to provide a corresponding crushing device which is suitable for crushing mineral and non-mineral substances by compressive load-application in one or more load-application stages with subsequent disagglomeration with a lower outlay on machines, and for achieving appropriate material throughputs with comparatively high energy utilization.
This object is achieved in process terms according to the invention by the measures according to claim 1 and in device terms with the measures according to claim 9. Advantageous designs of the invention are stated in the dependent claims.
According to the invention, the material to be ground consisting as a rule of fresh and recycling material, is removed by metered feed, preferably gravimetric, from a feed bunker by a grinding belt designed as a plate conveyor, subjected to loading by a hydropneumatically operated pressure roller and then dissaglomerated by a fast-running striking mechanism in the discharge area of the drive tumbler. By arranging a breaker rotor between the feed bunker and the pressure roller, a preliminary crushing can also take place of the material layer, or else, using a second pressure roller, e.g. instead of the breaker rotor, a preliminary load application or preliminary compression. The preliminary compression stage, which-is always connected to a ventilator for the material layer, can also be used to compact the material, applying suitably high pressures in the gap forming from the plate conveyor and pressure roller. A dissagglomerator can be dispensed with if the crushing device does not operate in a cycle with a separator and the final crushing takes place say in a downstream-connected tubular mill.
The device according to the invention consists of an elastically operated pressure roller which is preferably arranged vertically over the driver tumbler, also in the form of a roller, of the continuous plate conveyor, so that an adjustable gap forms between the pressure roller and the plate conveyor, in which the material layer located on the plate conveyor is crushed with subsequent disagglomeration by a striking rotor preferably arranged offset at 90xc2x0 in the rotation direction of the drive tumbler.
The solution according to the invention which realizes these features, has numerous advantages vis-à-vis high-pressure crushing rollers. In terms of process engineering, the advantages of the new crushing device, which will be called a belt roller mill in view of its structure and its mode of operation, are that the applied pressure levels can be freely adjusted, lie well below the pressures applied with high-pressure crushing rollers and the load is applied to the material layer in the compression section. For the crushing device according to the invention, pressures of 6 to 30 MPa are applied. For limestone of grain size K80 less than 40 mm and a hardness of 3.5 to 3.8 Mohs, pressures of 6 to 9 MPa are e.g. generally applied. The speed of the grinding path and the throughput are limited neither by the influence of inertia forces nor by the composition of the material to be ground nor by ventilation problems, so that the existing linear relationship between throughput and grinding path speed can be advantageously utilized in a wide speed range for regulating the throughput. With the circulating grinding path, which is designed as a plate conveyor, process operations such as bunker withdrawal, metered feed, drying or wetting can be combined, and the preliminary and fine-crushing with subsequent disagglomeration performed without intermediate transport apparatus in a single device. The metered removal of the material for grinding from the feed bunker as a defined material layer and its continuous supply to the grinding roller, lead to ideal load-application conditions, improve the material intake and deliver optimal conditions for carrying out the friction drive, i.e. for drive-less entrainment of the pressure roller by the contact with the material-laden plate conveyor.
The mechanical advantages of the belt roller mill are that it is easily repaired and maintained, all parts subject to wear are easily accessible and replaceable and longer service lives can be expected for all parts subject to wear as a result of using low pressure levels and determined movement patterns. In addition, the drive of the circulating load-application belt does not present any particular technical demands. For very high performances, it can also be designed as a double drive. The belt roller mill can be both mechanically and pneumatically connected to one or more separators in the cycle or also be advantageously used without a disagglomerator only for the preliminary crushing. By utilizing the modular properties of the belt roller mill, large material throughputs can be achieved by parallel installation, by a type of double-piston- or rotation-symmetrical arrangement of two, three or four devices.